The triploid hybrids are crosses between the tall, vigorous African marigolds and the compact, free-flowering French marigolds. Triploid hybrid marigolds are unable to set seed. As a result, plants bloom repeatedly through the summer, even in hot weather. One problem with the triploids is their low seed germination rate. Average germination is around 50 percent. Since the triploid hybrids are unable to produce viable seed, they also know as mule marigolds.
Signet marigolds (Tagetes tenuifolia) are quite different from most marigolds. Signet marigold plants are bushy with fine, lacy foliage. The small, single flowers literally cover the plants in summer. Flower colors range from yellow to orange. They are also edible. The flowers of signet marigolds have a spicy tarragon flavor. The foliage has a pleasant lemon fragrance. Signet marigolds are excellent plants for edging beds and in window boxes. The varieties Golden Gem and Lemon Gem do well in Iowa.
There are basically three planting options available to home gardeners when planting marigolds. Marigold seed can be sown directly outdoors when the danger of frost is past or started indoors 6 weeks prior to the last frost date. Marigolds are also available as bedding plants at garden centers.
Planting site requirements for marigolds are full sun and a well-drained soil. Plant spacing varies from 6 to 9 inches for the French marigolds and up to 18 inches for the taller African marigold varieties.
Summer care of marigolds is simple. Water occasionally during dry weather and pinch off faded flowers to encourage additional bloom. Tall African marigolds may require staking to prevent the plants from falling over or lodging during storms.
While marigolds are seldom bothered by insects and diseases, they are not problem free. Spider mites can devastate marigolds in hot, dry weather. Grasshoppers can also cause considerable damage. Aster yellows is an occasionally disease problem. In a related matter, some gardeners plant marigolds in their vegetable gardens to repel harmful insects. While the marigolds are an attractive addition to the garden, research studies have concluded they aren’t effective in reducing insect damage on vegetable crops.
Varieties of Marigolds
Bradford C. Bearce
Scientific Name: Tagetes sp.
Origin: South America-Argentina and New Mexico
Classification: Annual, herb
Use: Bedding plants, pot culture, edging, cut flowers
Height: 6 inches to 4 feet
Spread: 6 inches to 3 feet
Stems (Bark): Herbaceous
Flowers: Orange, yellow, mixed, red, cream and maroon; rounded or flat heads
Foliage: Lacy, feather-like, finely dissected, opposite, often pungent odor
Texture: Medium to fine
Growth Rate: Rapid
Soil Requirements: Good garden loam, moist, well drained
Maintenance: Keep soil moist but not wet. Remove spent flower heads for continuous flowering
Situation: Sun; flowering delayed if planted in shady areas
Insects & Diseases: Spider mites, spittle bug, aster yellows, wilt
Remarks: Propagate from seed sown indoors in March, April, or direct seed outdoors in May after danger of frost has passed. Planting
- Seed may be planted in seedbeds, coldframes, flats, clay pots, or peat pots.
- Pulverize the soil. Place the seed on the surface or in furrows and cover with 1/4 inch of perlite or vermiculite.
- Keep the soil moist and warm. The seed will germinate within a few days.
- When true leaves appear, the individual plants may be transplanted into individual 3-inch containers. Shade for a few days until the plants become established.
- Give the plants full sun.
- Plants will be ready to plant in the garden after the danger of frost has passed. Marigolds may be seeded directly into the garden after the danger of frost has passed. Follow the directions above as to preparing soil and seed depth. Seedlings may be thinned if necessary.
Other Varieties: There are many varieties of Marigolds and new ones are introduced each year. Various references group the species and varieties in many different ways, such as by size, (large, semi-dwarf, dwarf) or flower shape, such as chrysanthemums or pompon types, peony types and singles. However, for simplification, here, Marigolds are divided into four basic species: African Marigolds–Tagetes erecta; French Marigolds–Tagetes patula; Triploids–a hybrid (Tagetes erecta x Tagetes patula); Single Marigolds–Tagetes tenuifolia (signata) pumila. Within each of these species there are many hybrids producing variations in color and size.
African Marigolds–Tagetes erecta
Large flowered “African” or “Aztec” Marigolds— Plants are compact, erect, 12 to 14 inches tall; flowers to 3 1/2 inches across, blooms two to three weeks earlier than tall varieties, most flowers are doubles with flat or ball-like flower heads; colors range from primrose yellow through pumpkin-orange, no bicolors; used primarily as dividers; do not need to be staked as do tall varieties.
Tall–“African” or “Aztec” Marigolds–Large flowers in late summer to fall (short days determine flowering time), orange or yellow; plants attain heights of 3 feet or more and spread 3 feet; space plants 1 foot apart in groups of threes; should be staked or enclosed with wire up to 2 feet in height; used primarily for cutting.
French Marigolds— Tagetes patula
Large-flowered “French” Marigolds–Used primarily as a divider or bedding plant; medium height (12 to 16 inches and same width) spacing 8 to 12 inches; flowers are large, up to 2 inches in diameter; varieties include flowers which are doubled, large single daisy-like or supercrested.
Dwarf “French” Marigolds–Small plant up to 12 inches; flowers small (1 to 1½ inches across) in colors of yellow, gold or orange; continuous flowering from early summer to late fall, blooms may be crested, tufted, button or single types; some varieties are bicolored, yellow marked with brownish-red; two plantings may be needed as flowering becomes sparse during hot summer “dog days” from planting date.
Triploids (Tagetes erecta x Tagetes patula) hybrid
Triploids– a cross between “French” and “African” Marigolds; flowers about 2½ inches across and flower well during hot weather; flowers may be bicolored.